The present invention relates to a system for inspecting a completed air frame structure for cracks, more specifically such a system utilizing acoustic emission sensors to sense the formation or propagation of such cracks when the aircraft is subjected to force loading
Today's commercial aircraft are remaining in service longer than ever before. Factors contributing to this increase in the service life of such aircraft are the quality of the design and construction of such aircraft, the ever increasing costs of new aircraft to replace the older aircraft and the higher level of cost monitoring of the commercial airlines. The older aircraft may be continually updated by modernizing the electronics and avionics, as well as replacing and updating the interior of the aircraft to make the older airframe competitive with newer aircraft.
Inevitably, however, the older airframes will become increasingly vulnerable to metal fatigue cracks as their service life increases. Such cracks are formed in the metal as a result of fatigue or corrosion in the metal. Metal fatigue may be generated by the forces to which the metal is subjected during numerous take offs and landings, while corrosion may be caused by exposure to a corrosive atmosphere, such as operating the aircraft near large bodies of salt water. If the developing cracks remain undetected and are allowed to increase in size, they may be sufficient to cause the metal to fail at stresses below the normal yield strength of the metal. Such failure is the result of the resulting concentration of localized stresses above the yield strength at the location of the crack in the material. The larger the crack, the greater is the likelihood of the catastrophic failure of the material
In order to safely keep the older aircraft in operation, it is necessary to accurately inspect the entire airframe to detect and repair such cracks before they reach a level that could endanger the structural capability of the airframe. While it is known to use such inspection techniques as acoustic emission crack detection on individual aircraft components, such inspection techniques have not been applied efficiently to the entire airframe of a completed aircraft. The known inspection techniques typically require an acoustic emission sensor to be clamped or otherwise affixed onto the surface of the metal part being inspected, a requirement which would render the application of such sensors to the large surface area of a completed airframe time consuming and impractical.
While it would be possible to disassemble the aircraft and inspect each of its component parts, such an inspection technique would, quite obviously, be totally impractical on a commercial basis.
There is thus a need to provide an automated system for rapidly inspecting the completed major components of an aircraft airframe, such as the fuselage and wings, without requiring such elements to be disassembled.